Comparative effects of doxorubicin and a doxorubicin analog, 13-deoxy, 5-iminodoxorubicin (GPX-150), on human topoisomerase IIß activity and cardiac function in a chronic rabbit model.

Purpose A novel doxorubicin (DOX) analog, 13-deoxy, 5-iminodoxorubicin (DIDOX), was synthesized to prevent quinone redox cycling and alcohol metabolite formation, two prevailing hypotheses of anthracycline cardiotoxicity. The chronic cardiotoxicity of DOX and DIDOX was compared. Since a recent hypothesis posits that DOX-induced chronic cardiotoxicity may be mediated by inhibition of the topoisomerase IIß/DNA reaction, we also compared potency of DOX and DIDOX to inhibit topoisomerase IIß decatenation of kinetoplast DNA (kDNA) (a series or interlocking small rings of DNA). Methods We compared DIDOX with DOX to alter cardiac function in a chronic rabbit model. We also compared potency to inhibit decatenation of kDNA by purified topoisomerase IIß in vitro. Results DOX and DIDOX caused similar decreases in white and red blood cell counts indicating similar positions on the dose-response curve for cytotoxic efficacy. However, DOX but not DIDOX elicited a decrease in left ventricular fractional shortening and contractility of isolated left atrial preparations obtained at sacrifice. Histological scoring of apex and left ventricular free wall samples showed that DOX-treated rabbits had significantly more cardiac injury than samples from DIDOX or saline-treated rabbits. DOX inhibited decatenation of DNA by topoisomerase IIß with an EC50 of 40.1 µM while DIDOX did not have any apparent effect on topoisomerase IIß at the concentrations used in the study (0.1-100 µM). Conclusions Unlike DOX, DIDOX did not cause chronic cardiotoxicity and did not appear to interact with topoisomerase IIß in decatenation assays consistent with the hypothesis that inhibition of the topoisomerase IIß/DNA reaction may be a contributor of the mechanism of chronic DOX cardiotoxicity.

Phase I and pharmacokinetic study of the novel anthracycline derivative 5-imino-13-deoxydoxorubicin (GPX-150) in patients with advanced solid tumors.

PURPOSE: 5-imino-13-deoxydoxorubicin (DIDOX; GPX-150) is a doxorubicin analog modified in two locations to prevent formation of cardiotoxic metabolites and reactive oxygen species. Preclinical studies have demonstrated anti-cancer activity without cardiotoxicity. A phase I study was performed in order to determine the maximum-tolerated dose (MTD) of GPX-150 in patients with metastatic solid tumors. METHODS: GPX-150 was administered as an intravenous infusion every 21 days for up to 8 cycles. An accelerated dose escalation was used for the first three treatment groups. The dosing groups were (A) 14 mg/m(2), (B) 28 mg/m(2), (C), 56 mg/m(2), (D) 84 mg/m(2), (E) 112 mg/m(2), (F) 150 mg/m(2), (G) 200 mg/m(2), and (H) 265 mg/m(2). Pharmacokinetic samples were drawn during the first 72 h of cycle 1. RESULTS: The MTD was considered to be reached at the highest dosing level of 265 mg/m(2) since dose reduction was required in 5 of 6 patients for neutropenia. The most frequent adverse events were neutropenia, anemia, fatigue, and nausea. No patients experienced cardiotoxicity while on the study. The best overall response was stable disease in four (20 %) patients. Pharmacokinetic analysis revealed an AUC of 8.0 (±2.6) µg · h/mL, a clearance of 607 (±210) mL/min/m(2) and a t1/2ß of 13.8 (±4.6) hours. CONCLUSIONS: GPX-150 administered every 21 days has an acceptable side effect profile and no cardiotoxicity was observed. Further investigation is needed to determine the efficacy of GPX-150 in anthracycline-sensitive malignancies.

A phase II clinical study of 13-deoxy, 5-iminodoxorubicin (GPX-150) with metastatic and unresectable soft tissue sarcoma.

BACKGROUND: 13-Deoxy, 5-iminodoxorubicin (GPX-150) is a doxorubicin (DOX) analog synthesized to reduce the formation of reactive oxygen species and the cardiotoxic metabolite, doxorubiciniol, the two pathways that are linked to the irreversible, cumulative dose-dependent cardiotoxicity of DOX. In a preclinical chronic models and a phase I clinical study of GPX-150, no irreversible, cumulative dose-dependent cardiotoxicity was demonstrated. Recent studies suggest that DOX cardiotoxicity may be mediated, at least in part, by the poisoning of topoisomerase IIß. PATIENTS AND METHODS: An open-label, single-arm phase II clinical study in metastatic and unresectable soft tissue sarcoma (STS) patients was initiated to further evaluate the efficacy and safety of GPX-150, including cardiac function, specifically left ventricular ejection fraction (LVEF). RESULTS: GPX-150 was administered at 265 mg/m2 every 3 weeks for up to 16 doses with prophylactic G-CSF until progression, death, or patient withdrawal from the study. GPX-150 exhibited efficacy assessed as progression-free survival (PFS) rates of 38% and 12% at 6 and 12 months and an overall survival rate of 74% and 45% at 6 and 12 months. GPX-150-treated patients did not develop any evidence of irreversible, cumulative dose-dependent chronic cardiotoxicity. Toxicities included grade 3 anemia, neutropenia, and one grade 4 leukopenia. Correlative analysis demonstrated that GPX-150 was more selective than DOX for the inhibition of topoisomerase IIα over IIß in vitro. CONCLUSION: These results suggest future studies are warranted to further evaluate the clinical efficacy of GPX-150 in STS, perhaps at doses higher than 265 mg/m2 .

In vitro and in vivo immunosuppressive activity of a novel anthracycline, 13-deoxy, 5-iminodoxorubicin.

We report that the novel anthracycline analog, 13-deoxy, 5-iminodoxorubicin (DIDOX), represents a potentially new class of immunosuppressive agents. DIDOX has been structurally modified from the parent compound, doxorubicin, to remove the carbonyl group at carbon-13 and the quinone moiety at carbon-5 since these structures likely mediate the cardiotoxic side effects of this family of chemotherapeutic drugs. Our studies demonstrate that DIDOX inhibits T cell proliferation and the expression of the T cell activation molecules, CD25 and CD40L. DIDOX also inhibits the production of the pro-inflammatory cytokine, TNF-alpha and IL-2. Studies using animal models demonstrate that DIDOX inhibits the inflammation accompanying contact hypersensitivity reactions and possesses reduced cardiotoxicity compared to doxorubicin. These findings indicate that DIDOX has important immunosuppressive activities that may warrant the development of this new and improved anthracycline for the treatment of T cell-mediated inflammatory diseases.

Doxorubicin and C-13 deoxydoxorubicin effects on ryanodine receptor gene expression.

Chronic anthracycline administration to rabbits causes impairment of cardiac contractility and decreased gene expression of the calcium-induced calcium release channel of sarcoplasmic reticulum (SR), the ryanodine receptor (RYR2). The C-13 hydroxy metabolite (doxorubicinol), formed in the heart, has been hypothesized to contribute to anthracycline cardiotoxicity. C-13 deoxydoxorubicin is an analog unable to form the C-13 hydroxy metabolite. Therefore, doxorubicin, C-13 deoxydoxorubicin, or saline was administered to rabbits (1 mg/kg iv twice weekly for 8 weeks). Left ventricular fractional shortening (LVFS) was decreased by chronic treatment with doxorubicin (28 +/- 2%; P < 0.05), but not C-13 deoxydoxorubicin (33 +/- 2%) compared to age-matched pair-fed controls. Doxorubicin, but not C-13 deoxydoxorubicin, caused a significant reduction (P < 0.02) in the ratio of RYR2/Ca-Mg ATPase (SERCA2) mRNA levels (0.57 +/- 0.1 vs 1.22 +/- 0.2, respectively) in the left ventricle. This suggests that doxorubicinol may contribute to the downregulation of cardiac RYR2 expression in chronic doxorubicin cardiotoxicity.